The invention relates to a device and a method for the decontamination of hollow objects such as container caps by application of ultraviolet (UV) light.
The field of the invention is the decontamination of containers for the packaging in food and drugs industries.
The decontamination of containers by application of pulsed or continuous UV radiations is a well known technique, widely used in particular in the food and medical industry.
The technique exploits the ability of UV radiations to destroy cells and microorganisms, which is essentially due to two effects: a photochemical effect and a photothermal effect.
The photochemical effect, which is obtained with pulsed and continuous UV radiations, results from the absorption by the microorganisms of the UV radiation. It causes breaches and formation of abnormal bonds in the DNA molecules which prevent proper DNA replication. The microorganism's protein production and cell metabolism is blocked and it dies.
The photothermal effect is obtained with pulsed light, and results from the delivery to the microorganism of a high energy in a very short time. The radiations absorbed by the microorganisms causes a steep increase of the internal temperature and breaches of the cells membranes, without heating much the environment.
Decontamination by UV radiations is in particular used in the food industry for the decontamination of containers for food products, such as bottles and caps, prior to their filling. This decontamination is necessary for the good preservation of the packaged products.
The containers are exposed to a UV radiation in the production line, to destroy to the desired extent or level of decontamination the microorganisms on their surfaces.
We know for instance the document US 2007/0258851 from Fogg et al. which discloses a method for sterilizing containers and caps using UV radiations.
One problem with the technique of decontamination by exposure to UV radiations is that all the relevant surfaces must be exposed to an adequate level of radiations, and depending on their shapes and materials (transparent to UV or not), it may be difficult to reach them. This problem becomes even more critical when high levels of decontamination are expected, by example for packaging products with extended duration of conservation. Furthermore, the whole object must be decontaminated, including the internal and external surfaces.
For instance, a level of decontamination of a surface of 5 logs means that no more than 1 over 100000 microorganisms potentially existing on the surface may survive to the process.
For the bottles or similar containers, the problem is solved in the prior art systems by introducing into these bottles light sources or reflectors, and/or using bottles or containers transparent to UV.
The case of caps or any other similar object with a complex or patterned shape is more complex. These objects need also to be decontaminated as they are also in contact with the goods (food, beverages . . . ), but they frequently comprise patterns or shapes which are difficult to expose to UV radiations. Furthermore, they are usually not transparent in the UV, as they are made of materials diffusing and/or absorbing in the UV.
Prior art devices for the decontamination of caps by UV radiations try to solve the problem of the complex shape by providing multiple illumination sources with various angles of incidence, moving the caps relative to the sources or providing and moving reflectors. This classical approach leads to complex systems which are still not satisfactory when high levels of decontamination are expected, because some areas are still not reachable by direct illumination (for instance the plug seal for the water- and air tightness of bottle screw caps).
It is an object of the invention to provide a device and a method for the decontamination of objects such as container caps, which allows high levels of decontamination of all surfaces.
It is another object of the invention to provide a simple, robust and of moderate-cost device for the decontamination of objects such as container caps, which brings a solution to the previously mentioned problems.
It is still another object of the invention to provide a device and a method for such decontamination, adapted for a use in production line.